Stratospheric vehicles, such as airplanes, have been proposed in recent years as platforms for communication repeaters which provide a variety of communication services. One type of vehicle which can be used for these platforms is a hydrogen powered airplane. The high density of hydrogen can achieve the long endurance at high altitudes needed for commercial communication systems. Compared to gasoline, hydrogen, when combined with atmospheric oxygen, yields about three times the energy density of gasoline. The time aloft duration of airplanes fueled by hydrogen can be measured in weeks.
However, the use of hydrogen has disadvantages which make it difficult to realize the endurance advantage. Hydrogen, even in liquid form, requires a relatively large volume storage tank. Also, the low liquid temperatures required for hydrogen fuel systems necessitate a fuel tank that is well insulated. Due to these properties of hydrogen, conventional designs result in heavy tanks with the weight offsetting most of the endurance improvements that the energy density of hydrogen might provide. These tanks typically include metal shells of sufficient thickness to withstand the internal pressures and to be stable against buckling, and a surrounding solid or powdered insulation layer of a thickness adequate to control the heat flow into the tank from the surrounding environment. For a required storage time of several weeks, such a design results in a very heavy tank on the order of 100% of the weight of the fuel.
Thus, a need exists for a light weight cryogenic fuel tank designed to store hydrogen fuel in an airplane for communication repeater platforms.